The present invention is directed to hydrogen dispensing. More particularly, the present invention is directed to hydrogen dispensing algorithms for dispensing hydrogen from a source vessel to a receiving vessel.
Hydrogen dispensers for dispensing hydrogen into a receiving vessel are known. Prior art hydrogen dispensers are generally concerned with satisfying users by providing an algorithm for rapidly dispensing hydrogen to the receiving vessel, obtaining a complete and/or accurate fill in the least amount of time. It is desirable to satisfy users of the hydrogen dispenser.
Miller et al., U.S. Pat. No. 5,597,020, disclose a method and apparatus for dispensing natural gas with pressure sensor calibration. Miller et al. disclose that the user can input a total dollar amount of natural gas to be dispensed into his vehicle tank. Alternatively, the user can instruct the system to completely fill the vehicle tank.
Miller et al. state that the flow of natural gas through the sonic nozzle is controlled by a “digital” valve assembly. The valve assembly is referred to as a digital valve because it has only two positions—on and off. There are no intermediate positions typically associated with analog-type valves. The total amount of compressed natural gas dispensed is calculated based on the total cycle time and in accordance with the preprogrammed relation for mass flow through the sonic nozzle, both when the flow was choked and when it was not choked (i.e. subsonic), plus the small amount of natural gas that flows through the nozzle during the valve opening and closing times.
Miller et al. state that the dispensing system shown and described could be also used to dispense hydrogen or propane gas. While the user may have options to select an amount of natural gas dispensed, the user does not have any options for effecting the instantaneous natural gas dispensing rate. The instantaneous natural gas dispensing rate is fixed and controlled by the flow in the sonic nozzle and is not controlled by a programmable controller based on a user selection.
Compressed natural gas (CNG) dispensers are generally not used for dispensing hydrogen. In addition to differing safety issues, the Joule-Thompson effect causes the temperature in the CNG receiving vessel to decrease during dispensing, whereas hydrogen has a reverse Joule-Thompson effect where the temperature in the receiving vessel increases during dispensing. When dispensing CNG, the CNG temperature may decrease below the ambient temperature. The dispensing algorithm compensates for the temperature decrease of the CNG so that as the temperature of the dispensed CNG increases after dispensing, the pressure in the receiving vessel will not exceed the maximum rated pressure. Should this same algorithm be applied to hydrogen, having a reverse Joule-Thompson effect, the final density in the receiving vessel would be much lower than the rated density, resulting in an incomplete fill. Consequently, dispensing algorithms relating to CNG dispensers diverges from dispensing algorithms relating to hydrogen dispensers.
Whereas flow meters are commonly used in CNG dispensers, flow meters are generally not used for dispensing hydrogen. Currently available flow meters may not meet American National Standards Institute (ANSI) standards for dispensing hydrogen. Current methods measure the amount of hydrogen in a receiving vessel before and after filling to determine the amount of hydrogen transferred. The actual cost of the dispensed hydrogen to the customer may be determined after completing hydrogen dispensing. During hydrogen dispensing, a customer (user) does not have an indication of the “running” cost or instantaneous cost as a function of dispensing time.
It would be desirable to provide an estimated cost of hydrogen dispensing prior to dispensing hydrogen.
Those skilled in the art are searching alternative hydrogen dispensing methods.